* {
  box-sizing: border-box;
}

.rainbow {
  width: 400px;
  height: 400px
  border: 1px solid black;
  margin: 50px auto;
}

.rainbow div {
  overflow: hidden;
}    
.rainbow > div {
  width: 400px;
  height: 400px;
  background-color: red;
  border: 1px solid red;
  /* border-radius: 200px; */
}

.rainbow > div > div {
  width: 360px;
  height: 360px;
  background-color: orange;
  /* border-radius: 180px; */
  border: 1px solid orange;
  margin: 20px;
}

.rainbow > div > div > div {
  width: 320px;
  height: 320px;
  background-color: yellow;
  border: 1xp solid yellow;
  /* border-radius: 160px; */
  margin: 20px;
}

.rainbow > div > div > div > div {
  width: 280px;
  height: 280px;
  background-color: blue;
  border: 1px solid red;
  /* border-radius: 160px; */
  margin: 20px;
}
